The present invention relates to the field of optical data communication, computation, and data processing. More specifically the present invention relates to the more effective use of optical waveguides deposited on appropriate substrates to provide series of optical delay lines each line having longer delay than the last line by the same fixed constant. By optical switch selection of specific delay lines such optical delay networks can be used to provide commandable variable time delays such as can be used to coordinate the elements of phased array antennas for communication or radar applications. Alternately, optical delay networks can be used to time encode or decode pulse data. For example, many or all of the delay-lines can be used simultaneously to spread individual pulses into code division multiple access (CDMA) pulse patterns or to time correlate such pulse code patterns.
Various methods have been devised to provide time delays in optical data transmission. U.S. Pat. No. 5,109,466, issued to Kaltschmidt, describes a spiral optical waveguide formed of LiNbO3 deposited on a silicon substrate, the optical waveguide being interceptible at various points to detect an incoming signal at a predetermined delay. Secondary light waveguides in another plane guide light to the spiral delay line. The intent and design of the invention is for signal processing of incoming signals. The invention does not describe scalability, waveguide geometries with their design rules, nor the possibility of enhancing the real estate utilization by means of cross-over paths, nor the planar integration of functions, nor multiple inputs/multiple outputs.
U.S. Pat. No. 5,289,454, issued to Mohapatra, et al, describes a means, based on LiNbO3, or equivalent, switches, for directing a laser beam from one input to one of several outputs, or from one input to various outputs. The application is specifically for the interrogation of parallel data paths in an optical disk memory. The application does not require delays among the various branches of the tree topology. The switching is from within the structure of the invention.
U.S. Pat. No. 5,367,586, issued to Glance et al. on Nov. 22, 1994, describes a wavelength router, which is an optical wavelength analyzer, followed by a delay line array, which itself is followed by a wavelength combiner or coupler. The objective of the design is to stagger the sorted wavelengths by predetermined amounts prior to their being combined in a single output port. Thus, the input signals are sorted by wavelength and time slot.
U.S. Pat. No. 5,414,548 issued to Tachikawa et al. on May 9, 1995, describes an arrayed guide which is specifically designed to act as an optical wavelength sorter. This technique is an extension of the Dragone and Smit techniques for wavelength sorting or spectral analysis developed for telecommunications wavelength division multiplexing (WDM) wavelength sorting and routing.
U.S. Pat. No. 5,143,577 issued to Haas et al, describes a means of forming optical waveguides in optical polymers, such waveguides having a low loss property. Likewise, U.S. Pat. No. 5,519,803, issued to Shiono et al., describes a means to fabricate optical waveguides.
It is an objective of the present invention to provide a solid-state device based on optically transparent semiconductor or optical polymer materials capable of mapping an arbitrary set of inputs through a set of optical delays (ranging from about one picosecond to well beyond one nanosecond) to an arbitrary set of outputs. It is a further objective of the invention to accept multiple inputs and to distribute these to multiple outputs with a large dynamic range of delays, all delays being formed on a planar lightwave circuit by means of highly efficient, real estate conserving design algorithms. It is yet a further objective of the present invention that the delays of the invention be scalable structures usable by a control law and sometimes a set of external switches to effect various codes, states of a system, routes, etc. It is a still further objective of the invention that the topology of the structures be many-on-many to provide a wide variety of delay options independent of optical switching techniques, materials or processes. Finally, it is also an objective of the present invention that it can be fabricated with any of the techniques used to form optical waveguides of the kind described in the invention.
While some of the objectives of the invention can be found in the prior art, none of patents examined adequately satisfies all of the requirements described above.
L. Eldada, R. Scarmozzino, R. M. Osgood, Jr., D. C. Scott, Y. Chang, and H. R. Fetterman, "Laser-Fabricated Delay Lines in GaAs for Optically Steered Phased-Array Radar", J. Lightwave Technol., Vol. 13, p. 2034 (1995), show the construction of delay lines in an optically transparent semiconductor, the delay lines having an architecture of a single input split into multiple (8) outputs, each arm having a delta increase in delay, the right-hand arms having odd delays and the left-hand arms having even delays. The incremental delays were 3.4 ps. The splitting at each juncture was by means of an asymmetric coupling scheme.
M. -L. Wu, P. -L. Fan, J. -M. Hsu, and C. T. Lee, "Design of Ideal Structures for Lossless Bends in Optical Waveguides by Conformal Mapping", J. Lightwave Technol., Vol. 14, p. 2604 (1996), describe a methodology for designing curving optical waveguides in a planar structure which reduces the radiative losses of the waveguide.
L. Faustini, C. Coriasso, A. Stano, C. Cacciatore, and D. Campi, "Loss Analysis and Interference Effect in Semiconductor Integrated Waveguide Turning Mirrors", IEEE Photon. Technol. Lett. Vol. 8. p. 1355 (1996), describe the microscopic details of the turning mirrors for 90 degree turn optical waveguide structures to assure low loss turns.
R. Scarmozzino, "BeamPROP Version 2.0", RSoft, Inc., Montrose, N.Y., describes a computer aided design methodology and software for optimizing the optical transmission performance of complex optical waveguide structures made of optically transparent semiconductor or optical polymer processes and materials.
R. A Norwood. L. Eldada, S. Emo, J. Gustus, R. Rapoport, K. M. T. Stengel, L. W. Shacklette, C. Wu, C. Xu, and J. T. Yardley, "Polymer Optical Interconnection Technology: Toward WDM Applications", WDM Components Conf., SPIE Vol. 2690, p. 151 (1996), describe the materials and processes for producing optical waveguide structures, including delay lines, in optical polymers rather than silica-on-silicon, or optically transparent semiconductor materials
W. A. Wood, J. A. Chestnut, J. Hoffman, "Next Generation Shipboard Active-Array Radar Challenges", 7th Annual DARPA Symposium on Photonic Systems for Antenna Applications (PSAA-7), January, 1997, describe the requirements and applicable technologies for scalable delay line arrays in phased array radar applications.